Method of hardening and tempering steel.



J. M. LYNCH. v METHOD OF HARDENING AND TEMPERING-STEEL.

v APPLICATION I ILED APR. 23, 1909. 1,029,877.

2. K e m 6 .m A W m 00 5 M q m %WWNMWKfiW Mm/5355. [Mn $5M larly to a method of 31% PATNT JOHN M. LYNCH, OF BEVERLY, MASSACHUSETTS, ASSIGNOR' TO UNITED SHQIE: MACHINERY COMPANY, OF PATERSON, NEW JERSEY, A "CORPORATKON OF new JERSEY.

Specification of Letters Patent.

METHOD OF HARDENING AND TEMIPERING STEEL.

Patented June id,

Application filed April 23, 1909. Serial No. 491,732.

To all whom it may concern: Be it known that I, JOHN M, LYNoma citizen of the United States, residing at Beverly, in the county of Essex and State of Massachusetts, have invented certain Improvements in Methods of Hardening and Tempering Steel, of which the following description, in connection with the accompanying drawings, is a specification, like reference characters on the drawings indicating like parts in the several figures.

This invention relates to methods of hardening and tempering steel and particupartially hardening steel tools or other articles of substantially uniform composition throughout.

In the following description and claims the term tool will. frequently be used to designate the article "to be hardened, but it will be understood that by-the use of this term it is not intended to restrict the invention to hardening and temperingsteel articles properly designated as tools, and that the invention may be applied equally to hardening and tempering any articles of like material to which it is desired to give the characteristics which this method is especially adapted to give.

An object of the invention is an improved method of hardening and tempering steel tools, or other articles of substantially uni form composition throughout, by which a toolmay be produced which is hardened the desired distance back from its operating edge, withouta sharp line of demarcation between the hardened and unhardened portions. By such a method the strains usu- .al l.y left along this line in partially har- "dened tools, which have been hardened and .sliock resisting qualities and tempered by ordinary methods, maybe avoided and all-steel tools, having high tempered to meet the requirements of the work which they are to perform, may be produced.

Another object of the invention is a method of hardening and tempering by which a tool, having an operating edge of a particular contour, may be partially hardened in the manner above specified without affecting the contour of said edge.

A further'o-bject of the invention is a method of hardening and tempering tools, especially applicable to tools of the kind just described, by which a tool may be har-' with a back the cutting pressure. It is desirable that the dened and tempered in the desired parts tempering tools which consists in simultaneously heating different parts of the tool in mediums so arranged and of such relative conductivity that the part of that 001 to he hardened is heated to the desired hardening temperature and that the adjacent part is heated decrementally from the part to be hardened back and then immersing said tool while thus heated in a suitable hardening bath.

More specifically the invention comprises that improvement in the art of hardening and tempering tools of uniform composition throughout which consists inimmersing the part of the tool to be hardened in a metallic heating bath covered with a layer of heat conducting material of a depth and of a conductivity so related to the size and carbon content of the particular tool to be hardened that said tool will be heated decrementally from the immersed portion back, and then immersing said tool in a hardening bath.

As above suggested, the method of this invention is especially applicable to the hardening and tempering of tools having operating edges of predetermined contours and in practice it has been found especially useful in the hardening and tempering of stock cut-ting dies, such, for example. as those used wit-h the upper cutting machine known to the trade as the clicking machine.

For convenience of description and illustration the invention will be herein represented as applied to the hardening and tempering of diesof the type above referred to. These dies are of irregular shape, being designed tocut the different parts of the uppers of boots or shoes, and are provided with cutting edges which form closed outlines. Each die is usually provided also lying in one plane to receive cutting edges of these dies be comparatively hard and that the back, whlch is to receive the cutting pressure, or 1n the usual'practing edge of the die, after it has been shaped to the attern to be out, without distorting said'e ge and thereby causing it to depart from the pattern.

- The usual method of hardening and tempering these dies has involved heating the entire die to the hardening temperature.

' This practice is objectionable since internal hardening and tempering oper it is impossible cult to avoid strains are apt to be left in the die from its shaping operations and when the die is thus subjected to a high heat and sudden cold, to. foretell what the effect of these strains will be upon the final shape of the die. The reshaping of the die after "the tions has therefore involved considerable lbor and skill. Die making up to the pres at time has been a comparatively skilled art, requiring high priced labor, and one of the principal elements of skill involved has been, as above suggested, that required to reshape the die after it had been distorted by the hardening and tempering process.

An Tmpo'rtant feature of the-present invention is the novel heating step by which only that portion of the die which is to be hardened is heated to the hardening temperature While the. remaining portions of the die are heated decrementally from the portion brought to the hardening temperature, the heating being so graduated that no sharp line of demarcation between the hardened and unhardened portions of the die is left.- By the methods heretofore employed in hardening dies it has been difiithe formation of the line just referred to. Where it has been attempted to partially harden a tool by heating only the portion to be hardened to the hardening temperature, this line has still been formed, since the portion of the tool not to be hardenedhas been kept at a temperature considerably below that of the part to be hardened, whereby near the line between the two parts there would be a sharp change in the internal structure of the tool, thus causing the tool frequently to break at this point in use, even if cracks were not formed during the hardening operation. In other methods it has been attempted to effect a diflerential hardening of the tool by heating the entire tool to the hardening temperature and then quenching only the part of the tool which is to be hardened, letting down the hardness by the heat conducted from the unquenched portion and th n completing the cooling. This practice is as objectionable as that above referred to since the same sharp line is left between the hardened and unhardened portions of the tool as when the first described method is employed, and, furthermore, when the edge to be hardened has been given a desired outline this outline will usually be distorted, as above pointed out.

By the method of this invention the formatlon of the sharp line of demarcation between the hardened and unhardened portions of the tool is avoided by simultaneously heating different parts of the tool in mediums so arranged and of such relative conductivity that the part of the tool to be hardened is heated to the desired hardening temperature, which is preferably the highest transforming point of the steel employed, and that the adjacent )art receives a heat which gradually diminis es from the first mentioned part or, in other words, the tool is heated decrementally from the part to be hardened.

The method will now be described with especial reference to its'application to har dened and tempering shallow 'open dies of the type employed with the clicking machine. r

In the accompanying drawings,-Figure 1 illustrates suitable heating means for carrying out the method of this invention; Fig. 2 illustrates a convenient arrangement of the quenching or hardening bath for use in carrying out the method of this invention.

The dies are preferably made'of steelof uniform' composition throughout and the method will be specifically described with reference to its application to the hardening and tempering of. dies made from selecte billets of uniform open-hearth steel in which the accidental or injurious admixtures of hosphorus, sulfur, copper, arsenic, etc., are rcpt well below .05 per cent. in each case and in which the carbon content, from .60 per cent. to .90 per cent, preferably .80 per ce11t., is sufiicient to give the required edge holding capacity and, also, when tempered in oil, after having been hardened by the method of this invention, the highest possible shock resisting" qualities. The manganese content of the steel, from .30 per cent. to .50 per cent. is proportioned to give the highest possible welding power and also to exert the greatest influence on the change in volume and shape of the steel when hardened, of the outline of the dies.

The dies havin been made from steel of the composition .a ove indicated, preferably by the-method disclosed in United States Letters Patent No. 922,926 granted May 25, 1909, to J. M. Lynch for improvements in thus preventing shortening g be quickly raised to the ,5 posedot molten lead covered with a layer of charcoal of such a depth that the heat of v t i may be conducted to the part of the die adjacentto the part to be hardened to such an extent that said part will be heated decrementally from the part to be hardened back. A convenient bath is illustrated in Figl.

In suitable metallic receptacle 2, sup ported upon the brick lined frame l is a. lead bath ll covered with a layer of charcoal 8'.

A suitable grade of charcoal for covering the bath is what is known as P size charcoal, obtained from Wood alcohol works. The bath raised to the desired temperature by any suitable heating means, that herein illustrated comprising aburner 10 for an oil flame to which oil is flied through a pipe 12 cmitrolled by a valve 14, compressed an being conducted to the burner through an-' ther pipe 16 and controlled in amount by a valve 18. The lead bath is heated to a temperature somewhat higher than the highest transforming point of the steel in order that the part of the die to be hardened may desired temperature, and in tempering dies made of steel of the composition above indicated, the bath is preferably raised to a temperature of 1550" l which is preferably controlled by a py rometer,-the'highest transforming point of thesteel being approximately 1500". When hardening dies of the type employed with the clickin machine. which are com ara-v tirely light and about i of an inch in height, thecharcoal layer 8 is preferably of such a depth that only theupper edge or back of the die is exposed when the die is floated upon the bath. This edge is left exposed to permit the operator to locate the die when is he wishes to remove it from the bath. These dies when thus floated upon the bath will be immersed, about 3/16 ot an inch. The charcoal layer 8 has numerous functions, among which are to keep the surface a of the lead from oxidizing and to form a blanket bywhich the lQlllPQI'Zltlll'C of the bath, near its upper surface, may be kept 1h -h, the heat conductivity of the charcoal, iswell known, being less than that of the lead'fv tllheprincipal function of the charcoal cor ng, however, in the present method, is

cntuule variations in the ten'iperatorn between adjaceiizt portions of the die and larly to prevent a marked variation in the teurperatun between the inillleiscil portion and the :rl'ionlyingoutslde thclcu-zlhalli. 'ihistunc '1thecluucualcovraring; performs very satl ciorily wlrcn is made of a suitable depth slurp hvconduction 3 v-z uses the temperatures to which diii'erent cursin anyrpart 0f the die from the parts of the dies are heated to vary gradually from the part to be hardened toward the back or striking surface, whereby no sharp change in the internal structure ocpart to be hardened backto the striking surface which is left in an unhardened condition. There is thus no sharp line of demarcation between the hardened and unhardened parts of the die as in dies hardened and tempered by ordinary methods. r

The die shown at 20 in Fig. 1, having been floated upon the lead bath lon enough to bring the part to be hardene which includes its cutting edge, to the desired temperature, this being, as above suggested, preferably 1500", is then taken from said bath and immersed in the quenching or bardening bath, preferably oil, which may be contained-in any suitable receptacle, such for example, as that shown at 22 in Fig. 2. In practice this receptacle comprises the tank 22 containing cotton seed oil 24 which is kept stirred up and at a uniform temperature by jets of air taken preferably from a source of compressed air conducted down to the bottom through a pipe 20.

After the die has been heated and bardened in the manner described,tl1e hardness is let down or tempered in the following manner. The die is taken from the hardening bath and immersed in an oil bath with a thermometer attachment, said bath being at a comparatively low temperature at the time the dies are placed in it, for example, at a temperature of about 200. The die or dies, is then heated to the desired reducing temperature which in the case of dies made of steel of the composition above indicated and for the purposes for which these dies are intended is preferably 540. After the temper has thus been let down the dies are removed from the tempering bath and immersed in a cleaning bath consisting of a solution of caustic potash Ina ngtained at a temperature just below the boiling point by a thermostatic attachmentb Immersion of the dies in this bath prevents too sudden COOliIlg after they are removed from the tempering bath. After the dies have been washed in the caustic I potash bath, they are taken out and permitted to cool to the temperature of the room. The oil used in is preferably beef tallow.

\Vith dies of the sizes and composition above indicatcul the heating operation in th lead bath takes usually from to sec onds. It will therefore be seen that this method may be carried'mlt very quickly and very easily and with an assurance of substantially uniform results. The floating of the die upon the lead bath insures heating it back from its cutting edge tothc hardening temperature a substantially uniform disthe tempering bath tance throughout the extent of said edge. It will therefore be seen that this method is especially useful in hardening and tempering tools having cutting edges which form closed outlines especially where the cross section of the tool is uniform throughout its outline. The method may also be used to advantage in hardening other kinds of tools and, in fact, is thus em loyed. The depth of the layer of charcoa required to insure decremental heating from the part to be hardened back will vary of course with the size and carbon content of the tool to be hardened, the required hardening temperature varying with the carbon content of the steel. When the distance from the operating edge of the tool to the back is comparatively great, it will not be necessary to carry thel charcoal layer up to the back of the too It will be noted that an important advantage of this method when it is employed for hardening and tempering dies of the type above described is that in heating the die it may be floated upon the heating bath and that thereby the dimensions of the part of the die which is to be raised to the hardening temperature will be automatically determined. It will therefore be noted that the method contemplates heating a tool, having a cutting edge which forms a closed outline by floating the tool upon a heating bath having a specific. gravity so related to the specific gravity and structure of the tool that the part of the tool to be raised to the hardening temperature will be automatically immersed in the bath by the weight of the tool floating thereon.

Having described my invention, what I claim as new and desire to secure by Let tel-s Patent of the United States is 1. That improvement in the art of hardening and tempering tools which consists in simultaneously heating different parts of the tool in different contiguous heat conducting mediums .50 arranged and of such relative conductivity that the part of the tool to be hardened is heated to the desired hardening temperature and that the adjacent part is heated decrementally from the part to be hardened, and then entirely removing said tool from the heat conducting mediums and immersing it forthwith in a hardening bath.

2. That improvement in the art of hardening and tempering tools of substantially uniform composition throughout which consists in simultaneously heating different parts of the tool in different contiguous heat conducting mediums so arranged and of such relative conductivity that the part of the tool to be hardened is heated to the highest transforming point of the steel of which the tool is composed and that the adjacent part is heated decrement-ally from said first mentioned part, and then entirely removing said tool from the heat conducting mediums and immersing it forthwith in a hardening bath.

' 3. That improvement in the art of har. dening and tempering tools of uniform composition throughout which consists in immersing the part of the tool tobe hardened in a metallic heating layer of heat conducting material of a depth and of a conductivity so related to the size and carbon content of the particular tool. to be hardened that said tool will be heated decrementally from the immersed portion tgndhthen immersing said tool in a hardening at i 4. That improvement in theart of hardening and tempering tools of substantially uniform composition throughout, which consists in immersing the part of the tool to be hardened in a lead, heating bath covered with a layer of charcoal of a depth sufficient to conduct the heat of the bath to the tool decrementally from the part immersed and then immersing the entire tool in a hardening bath.

That improvement in the art of hardening and tempering tools which consists in immersing the part of the tool to behardened in a lead heating bath covered with a layer of charcoal extending to the upper edge of the part of the tool not immersed whereby said tool is heated decrementally from the immersed portion, and then quenching said tool by immersing it in a hardening bath.

6. That imprhvement in the art of bardening and tempering tools of uniform composition throughout, which consists in heating the part of the tool to be hardened to the highest transforming point of the steel of whichthc tool is composed by immersing said part in a metallicheating bath which is covered with a layer of heat conducting mabath covered with a 4 terial of a depth and of a conductivi so' related to the size and carbon content 0 the particular tool to be hardened that said tool will be heated decrementally from the immersed portion, immersin said tool in a hardening. bath and then'heating said tool in oil to temper it. I 7. That improvement in the art of tem pering tools, especially applicable to tempering tools having cutting edges which form closed outlines, which consists in fioating the tool edge down upon a metallic heating bath coa ered with a layer of material of lower heatgconductivity than the bath and of lesss ecific gravity than the tool, the depth an heat conductivity of said layer of material being su'fiicient to insure that the tool is heated decrementally from its immersed portiOmand then immersing said tool in a tempering bath.

8. That improvement in the art of tempering dies, especially applicable to tempering dies having cutting edges which form closed out-lines, which consists in floating the die edge down upon a bath of molten lead covered with a layer of charcoal extending to the upper edge of the die, whereby the die is heated for a short distance back from temperature, the heat gradually decreasing to the up )er or striking surface of the die, with 'no sharp line of demarcation between the part raised to the hardening temperature and the remaining portions, and then immersing S'tut die in ahardening'bath.

9. That improvement in the art of hardening and tempering tools having cutting edges which form closed outlines and having substantially uniform crosssection, which consists in floating the tool edge down upon a heating bath of a specific gravitysso related to the specific gravity and structure of the tool that the part of the tool to be hardened will be automatically immersed in the bath by the weight of the tool floating thereon while the remaining portion will be kept at a teu'lperature sutl'iciently below that of the immersed portion to maintain the outline oi the edge, and then immersing said tool in a hardening bath.

10. That improvement in the 'art of hardening and tempering tools, especially applicable to hardening and tempering tools having cutting edges which form closed outlines, which consists in floating the tool edge down upon a metallic heating bath covered its euttlng edge to the desired hardening with a layer of material of lower heat conductivity than the bath and of less specific gravity than the tool, the specific gravity of the bath being so proportioned to the specitic gravity and structure of the tool that -the part of the toolto be hardened will be automatically immersed in the bath by the weight of the tool floating thereon and the depth and heat conductivity of the covering material being such that the tool will be heated decrementally from the imn'iersed portion, whereby the tool may 'be allowed to remain stationary during the heating operatiomand then immersing said tool in a hardening bath.

In testimony whereof I have signed my name to this specification in the presence of two subsct'ibing witnesses.

JOHN M. LYNCH,

\Vitnesses:

II. Dousnr Srnxcnn,

LEONARD M. JoiiNsoN. 

